SAT Math · Linear functions · easy

The function f is defined by f(x) = kx + 7. If the graph of f is parallel to the line y = 5x - 2, what is the value of k?

The function ff is defined by f(x)=kx+7f(x) = kx + 7. If the graph of ff is parallel to the line y=5x−2y = 5x - 2, what is the value of kk?

Answer and explanation

Answer: B: 5

Parallel lines have equal slopes. The line y=5x−2y = 5x - 2 has slope 5, and f(x)=kx+7f(x) = kx + 7 has slope kk, so k=5k = 5, choice B. The different intercepts, −2-2 and 77, confirm the lines are distinct parallel lines and not the same line. Choice A (−5-5) has the slope of the opposite sign, which is a reflection, not parallel. Choice C (−15-\frac{1}{5}) is the negative reciprocal, which gives a perpendicular line. Choice D (15\frac{1}{5}) is the plain reciprocal, which gives neither parallel nor perpendicular. Parallel means the same slope.

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